When Nikolas Cruz started shooting last week at Marjory Stoneman Douglas High, an armed deputy stationed at the Florida school rushed to the building.
But instead of going inside, the officer waited outside for four minutes as the gunman killed students and faculty inside, authorities said.
School resource officer Scot Peterson never went in, despite taking a position on the west side of Building 12, where most of the carnage happened, Broward County Sheriff Scott Israel said Thursday.
"I think he remained outside for upwards of four minutes," Israel said Thursday in a news conference. The shooting, he said, lasted six minutes.
The sheriff came to the conclusion after watching surveillance video, talking to witnesses and getting a statement from Peterson.
"I'm devastated. Sick to my stomach. There are no words," Israel said. "These families lost their children. We lost coaches. I've been to the funerals, I've been to the homes. ... I've been to the vigils. It's just -- there are no words."
Asked what Peterson should have done when gunfire broke out at the Parkland school on February 14, Israel said the resource officer should have gone into the building.
"Addressed the killer. Killed the killer," the sheriff said.
Israel suspended Peterson without pay pending an investigation. Peterson chose to resign, he said.
CNN's calls to Peterson have not been returned.
New details about the massacre emerged Thursday, more than a week after 17 people died in one of the deadliest mass shootings in modern US history.
Years before Cruz targeted his former high school in Parkland, the sheriff's office had received 23 calls related to him or his brother, Israel said.
Some of the calls pointed to his potential for violence, making the sheriff's office the latest law enforcement agency to acknowledge it may have missed some warning signs. The FBI has said it failed to act on information about Cruz before the shooting.
During some of the calls, handled both in person and on the phone, deputies met with Cruz's mother.
Two deputies have been placed on restricted duty pending an internal investigation on how they addressed the warnings, Israel said.
"In two of these cases, after being briefed by internal affairs, I've restricted two of our deputies while we delve further into this, to take statements and make a decision whether or not they could have done more or should have done more," Israel said.
Jeff Bell, president of the Broward County Sheriff's Deputies Association, said his union is representing the two officers, and doesn't foresee any major problems with their handling of the calls.
He declined to discuss the particulars of the case, saying the investigation will focus on details of the calls to see what was reported and how it was followed up from there.
Peterson chose not to seek their representation, Bell said.
CNN also obtained records from the Palm Beach County Sheriff's Office that detailed deputies' interactions with Cruz in the home where he lived for a few weeks after his adoptive mother's death last year.
Two calls under review
The two cases under review are among 23 calls made to the Broward County Sheriff's Office in the past decade.
One call is from February 5, 2016 and the second was on November 30 last year.
In the 2016 case, officers received "third hand information" from a neighbor's son that Cruz planned to "shoot up" an unknown school. There was a picture of a "juvenile with guns" on Instagram, according to police records.
In that case, a deputy responded and determined Cruz had knives and a BB gun. The information was forwarded to a school resource officer, police records show. It's unclear whether it was Peterson. That case is listed as under internal affairs investigation.
In last year's incident, a caller warned in November that Cruz was collecting guns and knives, and wanted to join the Army. The caller said Cruz is suicidal and could be a "school shooter in the making," according to police records.
The report says that at the time, officers did not write a report on the tip. Cruz was no longer living at the listed Parkland address and lived in Lake Worth, Florida, according to police records. The deputy referred the caller to the Palm Beach Sheriff's Office.
That case is also listed as being under internal affairs investigation. The 21 other calls are listed as "no policy violation apparent."
More questions on response
More than a week after Cruz roamed the halls armed with an AR-15 style rifle, shooting and killing, questions remain on whether law enforcement agencies could have done anything to prevent the massacre.
When gunfire broke out, Israel said, Peterson was in a different building, helping resolve an unidentified issue with another student.
He rushed to Building 12, but did not go inside.
"I think he (Peterson) got on his radio at a point and time and he took up a position where it looked like he could see the western most entry into the building and never went in," Israel said.
Records show Peterson is a decorated officer who is respected by his peers. In 2014, he was awarded Parkland's school resource officer of the year while still stationed at Marjory Stoneman Douglas High School.
"During this time, deputy Peterson has proven to be reliable in handling issues with tact and judgment," the Broward Crime Commission said in the notation for the honor.
Before he was hired as a sheriff's deputy in 1985, he held several jobs, including working as a security guard, and also served in the military, according to his personnel records.
In 2015, Israel applauded Peterson's then-30-year tenure.
"Your dedication and allegiance are the best illustrations of the service [the sheriff's office] provides to the people of Broward County," Israel wrote, according to records.
Peterson also had two officer of the year recommendations.
Shooting footage not shown live
In yet another revelation, authorities said Thursday that surveillance footage from the school shooting was not shown live, as responding officers initially thought.
Police were watching it on a 20-minute delay, leading them to believe the gunman was still in the building when he was long gone, according to Coral Springs Police Chief Tony Pustizzi.
"The delay never put us in a situation where any kids' lives were in danger, any teachers lives were in danger," Pustizzi said at a news conference.
When officers arrived at the school, he said, they wanted to gain access to the security footage to learn what happened and where the perpetrator could be.
At some point, there was a miscommunication and officers believed they were watching real-time footage, he said.
"The issue was more of a communications failure on who was reviewing the tape, letting our guys know that it was a 20-minute delay in what they were reviewing," Pustizzi said.
The Sun Sentinel first reported the delay in surveillance footage.
In a statement, the Broward County School District said its security system footage could be reviewed in both real-time or be rewound to see events that were previously recorded.
"During the immediate response to the event, the system was being viewed in real-time and the recorded footage was being viewed to retrace the actions of the shooter," the statement said.
While the rewound footage might not have increased the number of casualties, it did hamper efforts to locate the gunman.
"Somebody would say, 'He's on the second floor,' and we had guys on the second floor saying, 'We're on the second floor, we don't see him,'" Pustizzi told the Sun Sentinel.
That's when officers figured out there was a tape delay.
Deputy Scot Peterson was outside building but "never went in," sheriff says
Peterson resigned after the revelation Thursday